<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>head</title>
</head>

<body>
    <div>打开浏览器控制台查看结果</div>
    <script>
        const head = arr => (Array.isArray(arr) && arr.length ? arr[0] : void 0);
        console.log(head([1, 2, 3]));
    </script>
</body>

</html>